Electric control



Mm W, 1.950 w. E. WINTERHALTEH ET m. 2,494,522

ELECTRIC CONTROL 2 Sheets-Sheet l Filed sept. 26,. 1945 www am.. 3% 1950 W. E. WIMTERHALTER m m.. 2A452 ELECTRIC CONTROL 2 SheetS-Sheet 2 Filed Sepc. 26, 1945 liu-Vif v Y l CJ W5 w www ,fw um w wn @iw W@ m www T m M,

Patented Jan. 17, 1950 ELECTRIC CONTROL William E. Winterhalter, Coshocton, `Ohimand Edwin E. Vonada, McKeesport,Pa.

Applicationseptember 2.6, 1945, Serial No. 618,664

(Cl. 20d-211) ll Claims.

fThisinvention relates to an electric control and primarily to the control otthe low .voltage high current systemlv/hich isused inmaintaining the ratio rof plating current to speedn necessary for producing uniform coating thicknesses in variablevspeed electroplating processes. Electrolytic tiri istrip `isordinarih7 produced. in` a continuous processing linelwhere `the speed-oi the strip` varies and this makes it `necessary` to change the current density in` synchronism with changes in speed ofn strip travelsoli that the weightlof. deposited `tin can be held constant. During constant speed operation the current density will vary d-ue tot differences in` the` temperature of the electrolyte, anode `corrosion and electrode spacing Variations caused by imperfect strip shape. Various means have been used to control therplating current in accordance withchanges in strip `speedbut such controls have not proved entirely'satisfactory.

"In thisA and othercontrclsi ithis necessary to provide a `circuit `for impressing upon aleld a voltage-proportional to the current orv-olta-ge` to be controlled. 4Such circuitsnow inluse have not proved-satisfactory `for all values of currents andvoltages which aretobe controlled.

Itis` an object of this invention to provide a control which will `permit accurate Acontrol of the weight of coating on the strip.

Another object is to provide apickupcircuit which is adapted for useinthe controlof our invention.

Still another object is to provide a pickup circuit which is adapted for use in controlling the currentoi-highor low D. C. current and voltage :v`

systems;

AThese and other objects will be more apparent after referring tothe `following specication and attached drawings in which:

Figure l isa schematic view showing the control applied to the electrotinning apparatus;

`Figure 2l is a schematic wiring diagram of a second circuitfor obtaining ithe1restraintvoltage;

Figure 3. shows the. wave form of the voltage acrossthe voltage divider of vFigure 2;

Figure 4 shows the output wave form of the audio -arnplier of Figure 2 Figure 5 shows the wave form of the rectified current of Figure 4; and l Figure 6 is a .curve showing` `the relationship betweenthel shuntmillivolts and the voltage output of the .current limiting circuit.

Referring more particularly to the drawings, the reference numeral 2 indicates aplatingtank which containsaa suitable electrolyte. The strip Spasses. from an uncoiler 4 over conductor roll Gland-thence intoithe tank 2 and passes out of the tank x over a conductor roll Si :from` which` it isd'irectedihy means oi a billy roll i0 into the driven puller rolls l2. As` the strip passes through y the`4 tank, .it is. directed between anodes l4..by means oi` sink rolls4 |61 and conductor rolls l8r.A 'Platingfcurrent issuppliedto the. plating tank from, atop plating generator 2d and albottomfplating generator 22. The positive terminal of generator Zilis connected to apositive bus bar 24Lv.which is connectedto` the anodes M which act upon the top of the strip. Generator 22 is con nectedinulike `manner to a positive bus bar 2li which is connected to the anodes lli acting upon the` bottom of the strip. `The generators 2E] and 22 .have common` negative connections and are connected to the negative bus `bar 28- which is connected to the conductor rolls 6, 8 and Hl.

'A saturable core reactor 30 is installed around thenegative bus 28` for a purpose which will be described later; Avshunt 32 is also installed in the negative bus for measuring the total plating current and for fthe control purpose described hereinafter.

`*Eieldm of generator" 29, and eld 36 of gen"` erator"22, are connected in parallelacross the armature of ai plating exciter 38 and are provided with hand operated rheostats 4i) and #32 connected in series with the respective elds t0 provide `top` and bottom current density balance. The apparatus described above is standard equipmentwith the exception of reactor .':land shunt 32. rIhese are used in the control of our inventiorrwhich exercises supervision over the armaturevoltage of the plating exciter 33 by varying its eldhM. The excitation circuit 45, il and 48 ot the-exciter 38 is connected across the armatureoroutput circuitoi a single unit` ampli- Tying exciter Ell through a current limiting resistoriu52. The excitert may be of the type known. as` the Amplidyne which is provided withr a plurality of field circuits wound on common pole pieces. The armature or output voltage ofthe exciter 5i! is principally derived from andcontroHed by two of theseelds E@ and 5B.

."Field 54 `is in the basic. control circuit 58 which is-:.connected` to produce a positive flux which increases the; output voltage of exciter 50 and consequentlylthe plating current as the line speed increases.` A tachometcr generator BH1 connected to be drivenby rolls I2 is located in this circuit and the output voltage of the generator is applied td field: 54; tlimu'ghA a current limiting resistorrEZ and a manually operated rheostat 64. This rheostat is used to accommodate plating current requirements when product schedule changes in electrode areas and coating weight occur. The tachometer generator 50 has the usual straight line speed voltage relationship.

Field 56 produces a restraining flux which is proportional to the total plating current and is in opposition to that of the basic control eld 54. The eld 56 is energized from a 110 volt A. C. source 58 through a pickup circuit 55 comprising a saturable core reactor 30, full wave rectier l and resistance l2. The saturable core reactor 30 is constructed by surrounding the negative bus 28 with a closed magnetic circuit of laminated silicon steel 74. An insulated 1450 turn coil 'F6 is Wound on this magnetic core and is connected to one side of the 110 volt supply and rectifier l0. The reactor 30 is designed and constructed so that with zero current flow in the negative bus 28 the impedance of the coil 'i6 will limit the current through field 56 to a very low value. When current flows in the negative conductor, a saturating flux is produced in the core l which decreases its effective permeability which in turn decreases the inductive reactance of coil 75, thereby increasing the current in field 55. Small changes in plating current produce opposite changes in the reactance of coil 'i6 which in turn causes the current through field 55 to vary with changes in plating current. Since this eld is in opposition to basic control field 5t, the output voltage of exciter 50 varies inversely as the plating current changes and will cause the plating generators and 22 to correct the current change. A condenser 18 may be used across coil l5 for power factor and Wave form variation, or in other words, for adjustment of strip speed-plating current characteristic shape. A resistor is connected across the D. C. terminals of rectifier l0 to load up the reactor so that regulation will occur on the straight line portion of the saturable core reactor saturating current impedance curve. An automatically variable by-pass resistor 82, such as the General Electric Control Thyrite, is connected in parallel with resistance 80 and provides additional means for varying the speed-plating current relation to any desired correction. Resistance 12 is adjusted to limit the current in circuit B6.

When the line speed is increased or when other changes are taking place, the output voltage of exciter 50 increases rapidly due to increased excitation from fleld 50 which is not immediately restrained by field 56. Likewise, when the line speed is decreased, the output voltage of exciter 50 decreases rapidly due to the decrease of excitation from field 55 which causes an immediate excess of current in field 56. These rapid changes cause a fluctuating of the control as it seeks to establish the desired relationship between line speed and plating current. In order to effect a smooth transition to steady conditions from the transient conditions in which high forcing power has been applied by the exciter 50 to the exciter 38, a stabilizing circuit lli having field therein is connected across the exciter 50 through direct current impulse transformer 88. A resistance 90 is employed in the line to adjust the magnitude of the secondary impulse from the transformer 88 to effect the stabilization desired. The polarity connections of eld 88 are such that the rapid increase of the output voltage from exciter 50 induces a delayed D. C. impulse voltage in the secondary of transformer 88 which is applied to l, normal line speed.

circuit 84 in opposition to the increased total excitation of exciter and tapers the output voltage to the steady conditions after the desired ratio of line speed and plating current has been established. In like manner, a delayed D. C. impulse voltage having a polarity opposite to that associated with line acceleration is induced in the secondary of transformer S5 which is applied to circuit when there is rapid deceleration and this brings the output voltage of exciter 50 back to the steady conditions after the desired ratio between line speed and plating current has been established.

In order to compensate for the small leakage excitation of circuit 65 when there is no excitation in circuit 58, circuit Q2 having field 94 therein is provided for exciter 50. The leakage current in circuit 55 overcompensates the normal residual voltage of exciter 50, exciter 3S, and generators Ze and 22 and causes reverse plating current to flow. That the strip S will become anodic and Will be subject to anodic corrosion. To prevent this anodic corrosion, eld is energized from a source of constant D. C. voltage and the desired amount of correction is obtained by adjusting the taps of resistor S5 so that the plating current is adjusted to zero where it will remain until circuit 58 is energized. The flux of eld 94 opposes that of field 56, but is so small that its eifect is negligible when the line is in operation.

When the line is operating at a particular speed with the plating current constant, the adjusted algebraic summation ratio of control fields 54, 5G and 94 determine the output of exciter 50. The exciter Eil has an amplification factor of from 1,000 to 10,000 and the algebraic summation of voltage is therefore .1% to .01% of the output voltage of exciter 50. Assuming that this output voltage is under steady conditions, the algebraio summation of excitation voltages would be .02 volt for a regulator having an amplification factor of 5,000. Typical control voltages supplied to field 56 is .5 to 5 volts and to field 5d is 2.5 to 25 volts when the line is moving at 10% to 100% of It is therefore evident that the algebraic summation of excitation voltages is only a small percentage of the voltages applied to the control circuits of exciter 5D. A .02% variation in line speed or a .1% variation in plating current would cause a departure of .005 volt from the adjusted algebraic summation ratio which would result in a 25 volt change in the output of exciter 50 to the field 44 of plating exciter 33. Since the rate of change would be approximately 2,000 volts per second, this change would, in addition to forcing the plating generators 20 and 22 to meet the new requirements, supply a D. C. impulse to control circuit 84 to taper this forcing to termination when the adjusted algebraic summation ratio of exciter 50 control circuits has been re-established.

When the line speed increases, the speed oi tachometer generator 50 is also increased, thus increasing its output voltage. This increases the ilux of eld 5d thus camu-ig an unbalance of fiux ratio produced by elds 54 and 55. This causes a rapid increase in output voltage of exciter 55 which is not immediately restrained by field 55. This in turn induces a delayed D. C. voltage in the secondary of transformer 88, which is applied to field 36 in opposition to the increased total excitation of exciter 50 and tapers the output voltage to steady conditions after the desired ratio of line speed and plating current has been established. The increased output of exciter 50 is supplied to andasse the `:ielch"orcexciter `3Brfthusincreasing .the outputl ot generators 20 and 22; Thischanges ithevim pedance.E oil` i coil 6 `"which` increases the flux of elde `to` establislfrlia new i relationship; between y fluxes produced` by.. fields 54 -andito provide the necessary increase `fin.r ltotaltrlux.Y When -the i line i speed decreases, Athetrluxproducedby iieldA will be l proportionately greater "than that producedrby field Sill-fandtthe outputlo-,exciter50Will beide-l.

creased, thus changing lthe output .ofi exciter.- 30

whichwin lturn changea` Hthe-l output ofi generators4 2||ar1do22,- This fchanges` lthe impedance ofcoil 1 16.u which decreases the flux Oilfield-50 toestablish a new relationship` between the :fluxes producedby iieldsi54 `and r5|ito` provide `the necessary decrease inttotaliflux.`

Figure 2 discloses a secondmethod-oobtaining therestraint Voltage.v In this :embodiment-the voltage. drop .-across thetplatingf-current negative conductor. shunt 32is used tor varying theexcitationtof held `56. Theflow shunt voltage-is ampli-` fied` `totthe desiredregulatingcsystem `,voltage by means tot. an `C..e1ectronic Mamplierl 98. .f An A. 5C. ampliei' isA usedrbecause the inherent instability .ofa D... C,.electronic amplier is obj ectionable. Thisnpickup Jcircuit willtbe Adescribed withreference -towa fspeciali-iapplication in which a 110 volts, 60 cycle .power supplyxsrtransformed to 2.5 volts by means of transformer |02. A full wave rectier lMlconyertsltheSOcycle sine wave to 120 unidirectional impulses per second. Two circuits emanate from the positive terminal of rectifier |04. The current of 'one circuit passes through the'shunt32iila xhalfi` wave rectifier |06 through .voltage divider |08 tothe center tap.,| l0.,y

and` thence to the negative terminal of,recti'er |04. The current 'of 'the othr,.ci1cuit` passes through resistor I |2,"" half 'wave rectifier lli through yoltage divider |08"t`oy th centen tapfi l 0 andLthence to the negative terminal of mrectiei |041 The half "wave rectiiiers |0|l and` 3| |`4 -are constructed tov afford very lo`W resistanccltocur-` rentk'iiow in" the" direction described above, but willprovide"'the' usual blocking of any current tending to flow in the opposite direction. This prevents the current caused by the shunt millivolts from flowing through the circuit comprising rectifier |06, voltage divider |08, rectifier ||4, resistance ||2 and back to the negative terminal of the shunt. The low impedance winding of a bridging input transformer IIB is connected across voltage divider |08 and couples the carrier to amplifier 98. The pulsating unidirectional input voltage is greatly amplied by amplifier |38 and is converted into a pulsating unidirectional voltage by rectifier IIB before it is impressed on held 56. With no plating current, resistor ||2 is adjusted until the voltage between points and |22 of voltage divider |08 is zero. In such case, the voltage wave form is that shown at A in Figure 3. When plating current through the shunt is raised to of the shunt rating, the wave form of the voltage across |20 and |22 will be as shown at B in Figure 3 with the polarity of the shunt leads as shown. The magnitude of this voltage will be equal to the millivolts and exists as pictured because the instantaneous voltage at 20 at zero time is below that at |22 by an amount equal tc the shunt millivolts. The maximum voltage is reached when the instantaneous voltage at |20 reaches the zero axis. 'I'his maximum Voltage is maintained until the instantaneous Voltage at |20 again crosses the zero axis. The negative maximum voltage is again reached when the instantaneous voltage at |22 reaches zero. If

6i: the 1 plating currentis increased ,-to `100% of' the4 shunt rating, `the wave form ofsthewvoltage be-'- tween |20 and` 22 assumes the shape shownxat'fCr irl-Figure 3. l The `increased magnitude iofthisu wave causes alinear increase in the.output.=volt.`` ageoi amplifier 98. i

The i approximate audio-ampliiier foutput 1 wave forms for the various l input.` waveforms shown'` in Figures are shownat A,\B andfClofr-Figurefli. The corresponding amplified `wave formafter rec--u` tiiication'is shown at1A, Band-C` ofwFigure =5 andtherelationshfip between the shunt millivolts i. andthewoltage impressed on field 56H18 l. shown in Figure 5.

Since thisA circuit `initially depends only gonx millivolt variations for its operation, the regulate-1` ing control system can be adapted to the current control of high or lowlD. C. current andcvoltage,` systems, while-the `corresponding control shown in Figure. l is adaptable only tohigh DC. currentsystems. Thcoperation of the control isi` otherwise thesame as that'described for-Figure l. i

Whilei.electrodepositionu of tin on steelostrip` has beenemployed to illustrate thecontro'landn circuits described, it islevident that theyiareapw plicable generallyto accurate continuouslysupereA vised i current regulation of i direct current mam chinos without use `of mechanical or othercontact: devices, excepting forfprotection.

While two embodiments fof: `the x inventionThayerr been shown and `describeduit` will".lbeoapparenti` that other adaptations andmodications mayrbef made `without' departing :from `the scope ofr` the following claims.

We claim:`

l. A pickup` and control circuitrcomprisingta saturableecre reactor having: a core and a coili` thereon, a direct current circuit `coupled Vto"sa'id1 core `for controlling .the` reactancerofrvlsaiducoilfl means for. connecting an .v alternating,currentf source to said coil, afull wave rectiii-er'connectedzf to said alternating .currentxsource saidlcoil beingu inL the `alternating l current `circuit .of i theirectier, a condenser connected across said coil, a control field connected across the direct current terminals of said rectier, a` resistor in said last named connection for loading up the reactor, and a by-pass resistor automatically variable in response to voltage across said control iield circuit, said by-pass resistor being connected in parallel with said rst named resistor, said condenser and resistances being proportioned to produce a linear result in the control field circuit.

2. Apparatus for electrically treating metal strip having an electrolyte therein, said apparatus including means for passing the strip through said electrolyte at a varying speed, an electric circuit including said strip and said electrolyte, electric powering means for supplying direct current to said circuit, a bus bar connected between said powering means and the strip, an amplifying exciter for varying the output of said powering means, a pair of fields for controlling the output voltage of said exciter, a saturable core reactor having a core surrounding said bus bar and a coil wound on said core, the current flowing in said bus bar controlling the reactance of said coil, a full wave rectiiier connected to an alternating current source and to said coil, a condenser connected across said coil, one of said control fields being connected across the direct current terminals of said rectifier, a resistor in said last named connection for loading up the reactor, a by-pass resistor automatically variable in response to voltage across said control field circuit,

said by-pass resistor being connected in parallel with said rst named resistor, said condenser and resistances being proportioned to produce a linear result in the control field circuit, means for producing a voltage proportional to line speed, and means for applying said last named voltage to the other of said fields to produce a flux in opposition to the iiux of the rst eld.

3. Apparatus for electrically treating metal strip having an electrolyte therein, said apparatus including means for passing the strip through said electrolyte at a varying speed, an electric circuit including said strip and said electrolyte, electric powering means for supplying direct current to said circuit, a bus bar connected between said powering means and the strip, an amplifying exciter for varying the output of said powering means, a pair of elds for controlling the output voltage of said exciter, a saturable core reactor having a core surrounding said bus bar and a coil wound on said core, the current flowing in said bus bar controlling the reactance or said coil, a full wave rectifier connected to an alternating current source and to said coil, a condenser connected across said coil, one of said control elds being connected across the direct current terminals of said rectifier, a resistor in said last named connection for loading up the reactor, a by-pass resistor automatically variable in response to voltage across said control field circuit, said bypass resistor being connected in parallel with said rst named resistor, said condenser and resistu ances being proportioned to produce a linear result in the control eld circuit, means for producing a voltage proportional to line speed, means for applying said last named voltage to the other of said iieids to produce a ux in opposition to the flux of the first field, and a third field for said exciter for producing a iiux to counteract the leakage excitation of the circuit of the first named iield when there is no excitation in the circuit of the second named eld.

4. A system for regulating the current output of a generator connected to a load including a moving metal strip, which system comprises a bus bar connected between the generator and the strip, an amplifying exciter for varying the output of said generator, a pair of fields for controlling the output voltage of said exciter, a saturable core reactor having a core surrounding said bus bar and a coil wound on said core, the current flowing in said bus bar controlling the reactance of said coil, a full wave rectifier, means for connecting an alternating current source to said rectifier and to said coil, a condenser connected across said coil, one of said control fields being connected across the direct current terminals of said rectifier, a resistor in said last named connection for loading up the reactor, a by-pass resistor automatically Variable in response to voltage across said control eld circuit, said by-pass resistor being connected in parallel with said rst named resistor, said condenser and resistances being proportioned to produce a linear result in the control eld circuit, means for producing a voltage proportional to strip speed, and means for applying said last named voltage to the other of said iields to produce a flux in opposition to the flux of the first iield.

WILLIAM E. WINTERHALTER. EDWIN E. VONADA.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,019,352 Livingston Oct. 29, 1935 2,278,151 Runaldue Mar. 31, 1942 2,325,401 Hurlston July 27, 1943 2,374,012 Hanna Apr. 17, 1945 2,374,199 Harris Apr. 24, 1945 2,404,948 Croco July 30, 1946 2,455,997 Holman Dec. 14, 1948 2,465,254 Edwards Mar. 1, 1949 

